First you have to know the frequency band that you need to jam, if you don’t know specifically as the transmitted signal hops between frequencies, so you need a jammer that can scan all the frequency band and send a jamming signal in all bands untill it found the transmitted signal hopping pattern.

Second, there are many jamming techniques such as narrow band jammer, wideband jammer, frquency hopped jammer , etc.

Finally you need to know how the transmission is done, on which frequency and if it hops or not.